The present invention relates to fiber optic networks, and more particularly to fiber optic wavelength add/drop systems.
Fiber optic networks are becoming increasingly popular for data transmission due to their high speed, high capacity capabilities. Multiple wavelengths may be transmitted along the same optic fiber. These wavelengths are sent combined as a single signal. A crucial feature of a fiber optic network is the exchange of wavelengths between signals on xe2x80x9cloopsxe2x80x9d within networks. The exchange occurs at connector points, or points where two or more loops intersect for the purpose of exchanging wavelengths.
The exchanging of data signals involves the exchanging of matching wavelengths from two different loops within an optical network. In other words, each signal would drop a wavelength to the other loop while simultaneously adding the matching wavelength from the other loop. The adding and dropping of wavelengths always occur together. Each wavelength is commonly referred to as a xe2x80x9cchannel.xe2x80x9d Add/drop systems exist at the connector points for the management of these exchanges.
FIG. 1 illustrates a simplified optical network 100. A fiber optic network 100 could comprise a main loop 150 which connects primary locations, such as San Francisco and New York. In-between the primary locations are local loops 110, 120 which connect with the main loop 150 at connector points 140 and 160. A local loop could be, for example, an optical system servicing a particular area. Thus, if local loop 110 is Sacramento, an optical signal would travel from San Francisco, add and drop channels with Sacramento""s signal at connector point 140, and the new signal would travel forward to connector point 160 where channels are added and dropped with local loop 120, and eventually to New York. Within loop 110, optical signals would be transmitted to various locations within its loop, servicing the Sacramento area. Local receivers 170 would reside at various points within the loop to convert the optical signals into signals in the appropriate protocol format. Loops 110 and 120 may also exchange channels directly with each other through a connector point 130 between them. An add/drop system would reside on loop 110 at the connector point 130 while a mirror image of the same add/drop system would reside on loop 120. Each loop includes an optical signal comprising channels xcex1xe2x88x92xcexn. If, for example, channel xcex2 is to be exchanged, loop 110 would drop its xcex2 while adding loop 120""s xcex2 to its signal. In the same manner, loop 120 would drop its xcex2 while adding loop 110""s xcex2 to its signal. Then each loop would transport it""s respective new signals to the next destination.
FIG. 2 illustrates a conventional add/drop system 200. First, the optical signal from loop 110 is separated into its individual channels by a wavelength division multiplexer 210A. The same occurs with the optical signal from loop 120 by the wavelength division multiplexer 210B. Each optical channel then travels along a separate optic fiber 260 to a receiver 220 which converts the channels into electrical signals. The electrical signals travel to the regenerator 230 which reshapes them to compensate for dispersions, gain loss, and attenuation. The regenerator 230 also comprises electrical switches which directs the proper electrical signals to be added/dropped. The add/drop function then occurs in the following manner:
Signals on loop 110 which are to stay on loop 110 are sent by the regenerator 230 to loop 110""s wavelength division multiplexer 250A.
Signals on loop 120 which are to stay on loop 120 are sent by the regenerator 230 to loop 120""s wavelength division multiplexer 250B.
Signals to be dropped from loop 110 (or added to loop 120) are sent to loop 120""s wavelength division multiplexer 250B by the regenerator 230. Loop 120""s corresponding channels to be added to loop 110 (or dropped from loop 120) are directed by the regenerator 230 to loop 110""s wavelength division multiplexer 250A.
Thus, the regenerator 230 functions similarly to a 2xc3x972 switch. In route to the correct wavelength division multiplexer, each signal is converted back into an optical channel by transmitters 240. The wavelength division multiplexers 250A-250D then recombines the channels sent to it into a single signal. The new signals for Loops 110 and 120 then continue to their respective next destinations.
A problem with conventional add/drop systems is the need to convert data signals sent in the optical domain to the electrical domain in order to effectuate the add/drop. Then signals must be converted back from the electrical domain to the optical domain before being transported to its next destination. Conventional add/drop systems are also cumbersome and inflexible due to the conversion requirement. Typically, the conversion required only allows the add/drop system to be operable for a particular protocol, at one particular speed, and for a certain number of wavelengths. If a different protocol is to be used, a faster speed is desired, or more wavelengths are to be added, each add/drop system along each connector point of the entire optical network 100 much be replaced. Since an optical network could comprise hundreds of connector points, the upgrading of a conventional add/drop system for an optical network is costly and difficult to do. What is desired therefore is a fiber optic wavelength add/drop system which does not have the optical to electrical to optical conversion requirement of the conventional systems. Thus, there is a need for an optical add/drop system which is programmable and which is simpler and more cost efficient to implement. The present invention addresses such a need.
An optical and programmable wavelength add/drop system for optical networks is provided. It includes the providing of a first optical signal on the first optical loop as a plurality of wavelengths, each wavelength residing on a separate path, such that the providing occurs in the optical domain; the reflecting of any of the plurality of wavelengths; the dropping of any of the plurality of wavelengths from the first optical loop into the second optical loop and for the adding of corresponding wavelengths from the second optical loop into the first optical loop, such that the dropping and adding occurs in the optical domain; and the combining of the reflected wavelengths and the added wavelengths into a second signal. With the add/drop system in accordance with the present invention, dispersion compensation, signal amplification, and gain equalization involved in the providing of the plurality of wavelength, as well as the switching function involved in the dropping and adding of wavelengths, may be performed without the need to convert the signals from the optical domain to the electrical domain and then back to the optical domain, rendering the add/drop system simpler and less costly to implement than conventional systems. The present invention has the added advantages of being capable of broadcasting and the monitoring of the adding and dropping of wavelengths individually. The programmable nature of the present invention reduces the required number of dense wavelength division multiplexers, and its modular design allows flexibility in upgrading to more complex systems.